Study About Transversal Deformation Properties Of Long-Span PC Box Girder Bridges

Due to the excellent structural behavior of box girder, it becomes more and more widely used in recent years. There was a mature approach for the analysis of box girder along the extent orientation of bridge. The longitudinal calculation is generally simplified as unit length of framework along the extent orientation of bridge, and then calculated by the finite element method of plane frame structures. And for transversal, only consider the affection of transverse distribution coefficient, no actual transversal calculations. This method is unable to know the transversal stress state of the section of box girder and to solve transversal reinforcement design. In the actual operation process, the phenomenon that the box subjected to eccentric load cracks is very common, especially for the roof box, longitudinal cracking is very common. Therefore, it is necessary to develop an accurate and convenient calculation program that can be directly used for the box transverse internal force in engineering design.Frame analysis is a method to transform three-dimensional problem into planar problem of box girder. In this paper, the basic method of plane frame analysis has been used to analyze the internal force of transversal frame in box girder. In order to know the transversal internal force of each section which is along the extent orientation of the bridge, we intercept the unit length of frame section along the extent orientation of the girder, take the angle(θ) of the two corners on the roof of the section and the four nodal displacements of the derivative(θ′) of the angle as the basic unknowns, and derive the relation between the nodal displacement of the section and the transverse bending internal force by using the method of displacement.Then, we take cubic polynomials as the displacement function, derive the horizontal frame element stiffness matrix using the principle of energy, and deduce the equivalent nodal forces under concentrated, uniform and weight loads respectively. Finally the calculation program is made in FORTRAN language. According to the calculation procedure, we can obtain the changing pattern of transversal internal force of box girder under the combination of various loads.In addition, this paper takes Yuanshui Bridge for engineering background, and the actual bridge models have been established. Then this paper compares the calculation results of actual bridge models with the regulation, relevant design material, actual existed problems of the bridges and relevant literature examples for analysis to prove the accuracy of the program calculation results. We arrange the vehicle loading on the most unfavorable position in the roof, compare the maximum transverse tensile stress of the roof that we have calculated and the lateral prestressing stress, and analyze the stress state of the roof of Yuanshui Bridge. Finally, the paper summarizes the shortcomings of the current design methods, and discusses how to prevent the problems such as craze on the top of the box girder.